Hooking Up a Portable Generator Safely: Inlets, Interlocks and Transfer Switches

A portable generator can keep the refrigerator, furnace, well pump and a few lights going through an outage. The problem is getting that power into the house safely. Extension cords through a window only reach a few things, and plugging a generator into a wall outlet with a “suicide cord” can electrocute a utility worker down the road, or you.

The safe way is a permanent connection: a generator inlet outside the house and either a panel interlock or a manual transfer switch. Here’s how they work and how to choose.

Why Backfeeding Is So Dangerous

If a generator is connected to your home’s wiring while the house is still connected to the utility, the generator’s power flows out through your meter and onto the lines. The transformer on the pole steps it up to thousands of volts. Line crews repairing what they believe is a dead line can be killed. When the power returns, it can also destroy the generator and start a fire.

Every safe hookup does one thing: it makes it physically impossible for the house to be connected to the utility and the generator at the same time.

The Three Parts of a Safe Hookup

1. A generator inlet box

A weatherproof inlet mounted on the outside wall, near where you’ll set the generator. You plug a heavy-duty generator cord into it instead of running cords through the house. Set the generator well away from the house, with its exhaust pointed away from doors, windows and vents.

2a. A panel interlock kit

A sliding plate on your main panel that lets either the main breaker or a dedicated generator breaker be on, never both. In an outage you turn off the main, slide the plate, turn on the generator breaker, then choose which circuits to run by switching breakers on and off within the generator’s capacity. It’s flexible and usually the lowest-cost option, but it needs a panel and breaker layout that accepts a listed interlock for that model.

2b. A manual transfer switch

A small panel next to your main panel with switches for a set of pre-wired circuits. Each switch selects utility or generator for its circuit. It’s simple to use in the dark, keeps you from overloading the generator, and works with panels that don’t accept an interlock. It covers only the circuits wired to it.

Sizing: What Can a Portable Generator Run?

Add up the running watts of what you want to power, then make sure the generator can also handle the starting surge of the largest motor (a well pump or a refrigerator compressor). Central air conditioning and electric water heaters usually exceed what a portable can carry. We help you choose the circuits that matter most for your generator’s size.

Code and Permits

Installing an inlet and interlock or transfer switch is new electrical work and generally needs a permit and inspection from your locality. The interlock must be a listed kit made for your panel, and the generator breaker and inlet must be sized for the generator. We handle the permit and inspection.

Running the Generator Safely

• Never run a generator indoors, in a garage, basement, crawlspace or on a porch. Carbon monoxide kills. Keep it at least 20 feet from the house with the exhaust pointed away.
• Install battery-backed carbon monoxide alarms on every level of the home.
• Let the generator cool before refueling, and store fuel safely.
• Keep the generator dry and on a level surface.

Have a portable generator but no safe way to connect it? Book a visit on our booking page and we’ll install an inlet and interlock or transfer switch.

Frequently Asked Questions

Is an interlock kit legal in Virginia?

Yes, when it’s a listed kit designed for your panel and installed with a permit. It is a recognized method of keeping a generator from backfeeding the utility.

Interlock or transfer switch, which is better?

An interlock lets you run any circuit in the panel, one set at a time. A transfer switch is simpler and limits you to pre-chosen circuits. We’ll recommend one based on your panel and how you’ll use it.

Can I just plug my generator into a dryer outlet?

No. A double-ended cord into an outlet backfeeds the house and the utility lines. It’s illegal, can kill a line worker and is a serious fire and shock risk.

Should I get a standby generator instead?

If you want the house to switch over automatically, or you lose power often, a home standby generator may be the better choice.

Why Homeowners Choose Progress and Heritage

Our licensed, insured, background-checked electricians install generator inlets, interlocks and transfer switches to code and show you how to use them before we leave. We serve Lynchburg, Bedford, Amherst, Campbell, Appomattox, Roanoke, Salem, Danville, Martinsville and the surrounding counties. See our residential installations and upgrades.